// 设置画布

const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');

const width = canvas.width = window.innerWidth;
const height = canvas.height = window.innerHeight;

// 生成随机数的函数

function random(min,max) {
  const num = Math.floor(Math.random() * (max - min)) + min;
  return num;
}

function randomColor() {
  return 'rgb(' + random(0, 255) + ', ' + random(0, 255) + ', ' + random(0, 255) + ')';
}

// Ball实例
function Ball(x, y, velX, velY, color, size) {
  this.x = x;
  this.y = y;
  this.velX = velX;
  this.velY = velY;
  this.color = color;
  this.size = size;
}

Ball.prototype.draw = function() {
  ctx.beginPath();
  ctx.fillStyle = this.color;
  ctx.arc(this.x, this.y, this.size, 0, 2*Math.PI);
  ctx.fill();
}

Ball.prototype.update = function() {
  if (this.x + this.size >= width || this.x - this.size <= 0) {
    this.velX = -this.velX;
  }
  if (this.y + this.size >= height || this.y - this.size <= 0) {
    this.velY = -this.velY;
  }

  this.x += this.velX;
  this.y += this.velY;
}

Ball.prototype.through = function() {
  if (this.x >= width) {
    this.x = 0;
    this.y = random(0, height);
  } else if (this.x <= 0) {
    this.x = width;
    this.y = random(0, height);
  }
  if (this.y >= height) {
    this.y = 0;
    this.x = random(0, width);
  } else if (this.y <= 0) {
    this.y = this.height;
    this.x = random(0, width);
  }

  this.x += this.velX;
  this.y += this.velY;
}

Ball.prototype.collisionDetect = function() {
  for (let i = 0; i < balls.length; ++i) {
    if (this !== balls[i]) {
      const dx = this.x - balls[i].x;
      const dy = this.y - balls[i].y;
      const distance = Math.sqrt(dx*dx + dy*dy);

      if (distance < this.size + balls[i].size) {
        balls[i].color = this.color = randomColor();
      }
    }
  }
}

const ballCount = 300;
// const speed = 5;
const minSize = 1;
const maxSize = 1;
let balls = [];
for (let i = 0; i < ballCount; ++i) {
  let size = random(minSize, maxSize)
  let speed = Math.ceil(maxSize/size);
  let ball = new Ball(
    random(0 + size, width - size),
    random(0 + size, height - size),
    random(1, speed),
    // random(1, speed),
    0,
    randomColor(),
    size
  );
  balls.push(ball);
}

function loop() {
  ctx.fillStyle = 'rgba(0, 0, 0, 0.25)';
  ctx.fillRect(0, 0, width, height);

  for (let i = 0; i < balls.length; ++i) {
    balls[i].draw();
    balls[i].through();
    // balls[i].update();
    // balls[i].collisionDetect();
  }

  requestAnimationFrame(loop);
}

loop();